1. Field of the Invention
The present invention relates to an electronic endoscope system for obtaining vascular information from an image captured with an electronic endoscope and a method for obtaining the vascular information.
2. Description Related to the Prior Art
Diagnoses and treatments using an electronic endoscope are very common. The electronic endoscope is provided with a long insert section to be inserted into a patient's body cavity. The insert section incorporates an imaging device such as a CCD in its distal end portion. The electronic endoscope is connected to a light source apparatus. Light emitted from the light source apparatus is applied to the patient's body cavity through the distal end portion of the insert section. The imaging device in the distal end portion captures an image of an objective tissue in the body cavity while the light illuminates the body cavity. The captured image is subjected to various processes performed by the processing apparatus connected to the electronic endoscope, and then displayed on a monitor. The electronic endoscope allows an operator to observe an image of the patient's body cavity real-time, which ensures accurate diagnosis.
A white light source such as a xenon lamp is used as the light source apparatus. The xenon lamp emits white broadband light in a wavelength range from a blue region to a red region. Illuminating the body cavity with the white broadband light provides an image showing an outline of an objective tissue. However, it is difficult to clearly observe microblood vessels, deep blood vessels, a pit pattern, an uneven structure such as a recess and a protrusion. It is known that illumination of narrowband light with a wavelength limited to a specific region allows clear observation of the above body sites. It is known that various pieces of information, such as oxygen saturation of hemoglobin in a blood vessel on an objective tissue, are obtained from image data when an image is captured with the illumination of the narrowband light.
For example, in U.S. Patent Application Publication No. 2003/0176768 (corresponding to Japanese Patent No. 3559755), three kinds of narrowband lights (red, green, and blue lights) are sequentially applied to a patient's body cavity as the illumination light. During the application of each narrowband light, an image is captured. Light reaches a deeper blood vessel as its wavelength becomes longer. For example, when the blue illumination light is applied, an image is captured with its surface blood vessel emphasized. When the green illumination light is applied, an image is captured with its middle blood vessel emphasized. When the blue illumination light is applied, an image is captured with its deep blood vessel emphasized. Color image processing is performed based on the image data of each of the captured images. Accordingly, in an image produced, the surface blood vessel, the middle blood vessel, and the deep blood vessel are shown in different colors so as to be easily distinguished from each other.
In Japanese Patent No. 2648494, narrowband lights IR1, IR2, and IR3 in a near infrared region are applied. The application of the narrowband lights IR1 and IR3 changes hemoglobin absorbance of a blood vessel due to oxygen saturation. The application of the narrowband light IR2 does not change the hemoglobin absorbance. During the application of each narrowband light as the illumination light, an image is captured. Changes in brightness of the images are calculated based on the images captured with the applications of the narrowband lights IR1 and IR3 and the image captured with the application of the narrowband light IR2. The calculated changes in brightness are reflected in black-and-white or in pseudo-color to the image. The information on the oxygen saturation of hemoglobin in the blood vessel is obtained from the image.
Recently, it has been desired to perform diagnosis and the like while the vessel depth and the oxygen saturation are obtained simultaneously. The hemoglobin absorbance of a blood vessel, however, changes considerably in accordance with a wavelength of the light applied (see FIG. 3). Accordingly, it is difficult to obtain information on both the vessel depth and the oxygen saturation simultaneously.
The sequential application of the three kinds of narrowband lights (the red, green, and blue lights) provides information on the depth of a blood vessel as described in the U.S. Patent Application Publication No. 2003/0176768, for example. However, the application of three kinds of narrowband lights does not provide information on the oxygen saturation. On the other hand, the application of the narrowband light IR1, IR2, and IR3 in a near infrared region provides information on the oxygen saturation as described in the Japanese Patent No. 2648494. However, the application of narrowband lights in the near infrared region does not provide the information on the depth of the blood vessel. The information on the vessel depth and the information on the oxygen saturation cannot be obtained simultaneously even if the lights in wavelength regions including both of the wavelength regions disclosed in the U.S. Patent Application Publication No. 2003/0176768 and the Japanese Patent No. 2648494 are applied.